This invention relates generally to an apparatus for dispensing particles of granulated material, and more particularly concerns a device for monitoring the quantity of particles stored in the dispensing apparatus.
In the process of electrostatographic printing, an electrostatic charge pattern or latent image corresponding to an original document to be reproduced is recorded on an insulating medium. A viewable record is produced by developing the latent image with particles of granulated material to form a powder image thereof. Thereafter, the visible powder image is fused to the insulating medium, or transferred to a suitable support material and fused thereto. This type of process was originally disclosed in U.S. Pat. No. 2,297,691 issued to Carlson in 1942.
Development of the latent image is achieved by bringing a developer mix into contact therewith. Typical developer mixes generally comprise dyed or colored thermoplastic particles of granulated material, known in the art as toner particles, which are mixed with carrier granules, such as ferromagnetic granules. When appropriate, toner particles are mixed with carrier granules, the toner particles are charged triboelectrically to the correct polarity. As the developer mix is brought into contact with the electrostatic latent image, the electrical field produced by the latent image causes the toner particles to transfer from the carrier granules and adhere thereto. However, as toner particles are depleted from the developer mix, additional toner particles must be supplied thereto. In this way, the concentration of toner particles in the developer mix is maintained substantially constant.
In the operation of an electrostatographic printing machine, it is highly desirable to have means for indicating when the supply of toner particles in the dispensing apparatus has become exhausted. This enables the operator to add additional toner particles thereto to maintain optimum machine reproduction characteristics. Heretofore, the level of toner particles in the dispensing apparatus was determined by the machine operator lowering a graduated rod into the toner particles which indicated the quantity remaining therein by the operator visually noting the level of toner particles remaining on the rod. However, due to their extremely small size, the toner particles tend to become air borne when the dispenser is opened. The air borne toner particles contaminate the surrounding area, blacken the operator's hands and clothing, and create, in general, undesirable working conditions. In addition, toner particles handled in this manner have a tendency to become electrostatically attracted to any machine components having a charge of opposite polarity thereto. An improvement over the aforementioned manual method of determining the quantity of toner particles remaining in the dispenser is by a suitable electrical switching arrangement. This approach has a disadvantage in that the toner particles, due to their small size, may contaminate the switch resulting in erroneous signals being generated thereby.
Accordingly, it is a primary object of the present invention to improve the toner dispensing apparatus of an electrostatographic printing machine by monitoring the quantity of toner particles stored therein.